This is a great example of the principle "don't just listen to your ear." As I was reading the sentence, I was thinking "the GMAT usually prefers constructions like 'powers that enable...'" But - just because that's the structure that most often shows up in right answers, it doesn't mean that other structures are wrong.

First, look for clear rule violations that you can eliminate:

By a vote of 9 to 0, the Supreme Court awarded the Central Intelligence Agency broad discretionary powers enabling it to withhold from the public the identities of its sources of intelligence information.

(A) enabling it to withhold from the public
(B) for it to withhold from the public
(C) for withholding disclosure to the public of
(D) that enable them to withhold from public disclosure
(E) that they can withhold public disclosure of

Some answer choices have "it"; others have "them." Since the Agency is singular (collective nouns = singular in American English), we cannot use the plural "they." Eliminate D and E.

In B and C, "award powers for" does not sound idiomatic. But you should ignore idiom issues until you've addressed all other meaning and grammar issues.

In C, "withholding disclosure of identities" is redundant. Eliminate.

Now that we have it narrowed down to A and B, ask if there are meaning differences between the two. When do we use a construction like "powers for"? Wonder Woman uses her powers for the greater good. We can understand this to mean "for the purpose of." The object of the preposition is the recipient/outcome of the powers.

In this sentence, the purpose / outcome of the powers is not to withhold information; that's part of what the powers are, not what they do. We have to choose "powers enabling," not "powers for."

The answer is A.